In the past, a variety of devices such as fluorescent lamps have been used as a white illuminating device. Recently, there have been developed new light sources such as inorganic ELs (Electro Luminescence), organic ELs (OEL (Organic Electro Luminescence) and OLEDs (Organic Light Emitting Diode)) and semiconductor light-emitting elements, which have been used for developing an illuminating device. For example, for an illuminating device such as an LED lamp using a semiconductor light-emitting element, the surface of the semiconductor light-emitting element is coated with a phosphor, or powder of the phosphor is contained in a resin constituting the LED lamp to practically realize other emission colors, for example white, than the original emission color from the semiconductor light-emitting element. In such illuminating device, a GaN-based semiconductor light-emitting element emitting blue light with a center wavelength approximately 460 nm is generally utilized. More specifically, the surface of the GaN-based semiconductor light-emitting element emitting blue light has a phosphor-containing layer containing yellow-light emitting cerium-activated yttrium aluminate (YAG) phosphor, and the phosphor-containing layer converts a light from the semiconductor light-emitting element to obtain white light.
For such illuminating device using such the semiconductor light-emitting element, there has been such a problem that the central part of the irradiation face looks blue and a yellow ring is produced at its circumference because of passing through the blue color of excitation light, resulting in uneven coloring and non-uniform white on the irradiation face.
To solve this problem, Patent Document 1 and Patent Document 2 propose a structure of disposing a lens having the central emission face with a convex lens shape to emit the emission light outside, and a structure of disposing a shading member to cut the outskirts part of the emission light, respectively.
Patent Document 3 proposes a structure of using a semiconductor light emitting element (LED chip) emitting ultraviolet light, a first phosphor layer comprising a blue-light-emitting phosphor absorbing the ultraviolet light and emitting blue light is formed on the LED chip, and a second phosphor layer comprising a luteofulvous-light-emitting phosphor absorbing the blue light and emitting luteofulvous light is formed on the first phosphor layer.
Patent Document 1: JPA 2005-216782
Patent Document 2: JPA 2005-243608
Patent Document 3: JPA 2000-183408